Mercury study set to take place in Clear Lake

CLEARLAKE OAKS -- A study will be conducted on contaminated sediments during the next two years regarding mercury levels in Clear Lake.

The U.S. Environmental Protection Agency (EPA) will build two test covers, also known as caps, at the bottom of Clear Lake near the shore as part of a remedial investigation for the Sulphur Bank Mercury Mine Superfund Site located in Clearlake Oaks.

A superfund is a site that contains toxic wastes the EPA has designated to be cleaned up.

The caps will help prevent mercury from migrating from sediments out into the water.

"The big part of the project will be monitoring the performance of these caps over the next two years," EPA site manager Gary Riley said.

About 20 people from seven subcontracting firms and the EPA will be involved in the process.

Each cap, approximately 120-feet by 100-feet, will have two 8-inch layers, one made up of sand and the other of gravel.

Sediment accumulated on top of the caps as well as water and small creatures at the bottom of the lake will be monitored and tested for mercury, Riley said.

Both caps will have monitoring devices installed and samples will be collected every six months, Riley said.

The samples will be compared to pre-baseline samples collected before construction of the caps.

"That will give us a good idea on how successful it is, and looking at the data will let us see how we can come up with a full-scale remedy," Riley said.

Contractors have prepared the construction staging area, and building will begin on Monday Jan. 7. Riley said the caps should take four to six weeks to complete.

"One goal over the next weeks is to determine how effectively we can construct these caps," Riley said.

The site is relatively remote and disturbance in the community is expected to be low.

The 150-acre site was mined for sulfur and mercury on and off beginning in the 1860s. The mine, once one of the largest produces of mercury in California, has been inactive since 1957, according to the EPA's website.

The agency found high levels of mercury in the bottom sediments in Clear Lake, as well as in the food web. The levels of mercury in fish from the lake have led to a state issued advisory to limit fish consumption from the lake.

Soils at the Elem Indian Colony, adjacent to the mine property, are contaminated with high levels of mercury and arsenic as well, according to the EPA.

Surface water and groundwater that discharge from the site contain high levels of mercury and arsenic and contaminate the natural wetlands to the north of the mine property and the sediments of Clear Lake, according to the EPA.

The construction and performance of the caps will help EPA members determine what can be done in the future.

Riley said if the caps are successful in preventing mercury from spreading into the lake, they will consider expanding the caps after the testing period ends.

Berenice Quirino is a staff reporter for Lake County Publishing. She can be reached at 263-5636, ext. 36 or at bereniceq.recordbee@gmail.com.